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An Artificial Leaf: a photo-electro-catalytic cell from earth-abundant materials for sustainable solar production of CO2-based chemicals and fuels

Periodic Reporting for period 3 - A-LEAF (An Artificial Leaf: a photo-electro-catalytic cell from earth-abundant materials for sustainable solar production of CO2-based chemicals and fuels)

Reporting period: 2019-07-01 to 2021-06-30

Mimicking the photosynthetic function of green plants and algae is one of the major technological challenges scientist around the world are facing nowadays. Natural photosynthesis transforms water (H2O) and carbon dioxide (CO2) into oxygen and carbohydrates using exclusively the energy of the sun. An artificial photosynthesis scheme will work in an analogous way, absorbing sunlight to combine water and CO2 into oxygen and chemicals, including fuels.
Fuels and fine chemicals are essentially produced from fossil reservoirs, whose retrieval and use have a deleterious impact on the environment. The combustion of fossil fuels (coal, oil and gas) is causing emissions of large amounts of “greenhouse gases” (GHGs) to the atmosphere, provoking global warming and affecting climate change.
A-LEAF European consortium seeks the realization of an artificial photosynthesis platform: for the capture and transformation of solar energy into chemical energy, as sustainable substitute for fossil resources.
Our multidisciplinary effort starts from atomic-scale studies to determine experimentally and theoretically the main parameters for optimization of the chemical transformations at surfaces to combine water and CO2 into oxygen and energy-rich chemicals. This knowledge will be transferred and up-scaled into (photo)electrochemical set-ups to maximize performance. The champion components will be combined into a single photoelectrocatalytic(PEC) device: an artificial leaf. Our final aim is to validate our strategy and approach with respect to technological and industrial parameters, to assess the comparative advantages and disadvantages for the incorporation of A-LEAF into an economically viable, and environmentally sustainable energy cycle.
At the end of the project we are happy to share the most relevant result from the different tasks:
WP1- Surface science : Spatially resolved experiments shed light on the electrocatalytic active surfaces, along their evolution under electrochemical conditions. We assessed at the nanoscale the stability and reconstruction of metal oxides for the oxide evolution reaction (OER): and of doped copper metallic surfaces for the selective reduction of CO2 to formate (CO2R).
WP2 . Electrocatalysis: Through electrochemical analyses, we selected the most promising catalysts, according to activity and stability, and the corresponding synthetic protocols. The catalysts were deposited onto electrode supports to analyze the optimum working conditions to drive the two chemical reactions, OER and CO2R. We found catalysts with great Faradaic efficiencies, well over 90%, in both cases, although with different electrolyte requirements.
WP3 – Theory: Computational analysis following the experimental results allowed us to determine key descriptors to drive energy efficient OER catalysis (lower overpotentials), and product selective CO2R (towards formate).
WP4 – Photoelectrocatalysis: Multiple architectures for Si-based photovoltatic layers were developed to be incorporated into photoanodes (or photocathodes). We engineered the deposition of the catalysts onto these Si light absorbers with appropriate interfaces to minimize energy loses between light absorption and electrochemical performance in our A-LEAF integrated system.
WP5 – An A-LEAF device: Gathering all knowledge, materials components and engineering tools as developed in the previous WPs, we designed and built a series of A-LEAF devices, matching the initial objectives as described in our original proposal: A photoelectrochemical (PEC) device, able to produce formate (formic acid) and oxygen from CO2 and water has been delivered, with a solar to fuels energy efficiency > 10%.
All our non-sensible results have been or are in the process of being published. Dissemination of the main results has taken place through open access publications and presentations in different international conferences and specialized workshops. Press releases have been sent out and pieces of news published in different media outlets.
Results susceptible of being commercially exploited will be protected before dissemination, and plans for exploitation have been drafted. One patent dealing with a combustion method to prepare electrodes has been filed as a result of the research of A-LEAF.
Among all specific scientific results, the most obvious progress beyond state of the art resides in the realization of a complete, and sustainable A-LEAF device. Our device represents a world-record for solar to formate efficiency, and will be listed as one of the devices with record solar to CO2-based fuels independent of the target product.
This achievement has been realized exclusively incorporating abundant and non-critical materials: carbon, silicon, copper, iron, zinc or nickel. Also exclusively employing scalable and industrially-accepted processing methods: thermal treatment at low pressure, adsorption processes, water-based washing and filtering, and non-toxic solvents. This technology is ready to move to the next step of scaling up to confirm its industrial relevance.